1. Field of the Invention
The present invention relates to a display device and a method of fabricating a display device, and more particularly, to an organic electroluminescent display (OELD) device and a method of fabricating an OELD device.
2. Discussion of the Related Art
In the past, many display devices have employed cathode-ray tubes (CRTs) to display images. However, various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and electro-luminescent display (ELD) devices, are currently being developed as substitutes for the CRTs. Among these various types of flat panel displays, the PDP devices have advantages of large display size, but have disadvantages of heaviness and high power consumption. Similarly, the LCD devices have advantages of thin profile and low power consumption, but have disadvantages of small display size. However, the OELD devices are luminescent displays having advantages of fast response time, high brightness, and wide viewing angles.
FIG. 1 is a schematic circuit diagram of an OELD device according to the related art.
As illustrated in FIG. 1, a gate line “GL” is extended along a first direction, and a data line “DL” and a power supply line “PSL” apart from each other are extended along a second direction perpendicular to the first direction. The gate line “GL”, the data line “DL” and the power supply line “PSL” define a sub-pixel region “SP”.
A switching thin film transistor “SwT” is disposed at a crossing portion of the gate and data lines “GL” and “DL” as an addressing element. A storage capacitor “CST” is connected to the switching thin film transistor “SwT” and the power supply line “PSL”. A driving thin film transistor “DrT” is connected to the storage capacitor “CST” and the power supply line “PSL” as a current source element. An organic electroluminescent (EL) diode “E” is connected to the driving thin film transistor “DrT”.
When a forward current is supplied to the organic EL diode “E”, an electron and a hole are recombined to generate an electron-hole pair through the P(positive)-N(negative) junction between an anode, which provides the hole, and a cathode, which provides the electron. Because the electron-hole pair has an energy that is lower than the separated electron and hole, an energy difference exists between the recombination and the separated electron-hole pair, whereby light is emitted due to the energy difference.
In general, both of an array element including the switching and driving thin film transistors, and the organic EL diode are formed on an array substrate, and the array substrate is attached with an encapsulation substrate. Thus, the production efficiency of the OELD device is reduced. For example, when one of the array element and the organic emitting diode is determined to have a defect after fabrication, then the array substrate is unacceptable and thus the production efficiency of the OELD device is reduced.
To solve this problem, a dual-panel type OELD device is suggested, where the array element and the organic EL diode are formed on different substrates.
FIG. 2 is a cross-sectional view of a dual-panel type OELD device according to the related art, and FIG. 3 is a cross-sectional view of a data pad area of the dual-panel type OELD of FIG. 2.
As illustrated in FIGS. 2 and 3, first and second substrates 1 and 71 face and are spaced apart from each other. In the two substrates 1 and 71, a display area “DA” for displaying images and a non-display area “NA” surrounding the display area “DA” are defined. A seal pattern 93 attaches the first and second substrates 1 and 71 in the non-display area “NA”. An array element including a driving thin film transistor “Tr” and a switching thin film transistor (not shown) is disposed in a sub-pixel region “SP” on the first substrate 1. An organic EL diode “E” is disposed on the second substrate 71 in the sub-pixel region “SP”. The organic EL diode “E” includes a first electrode 75, an organic emitting layer 87 and a second electrode 90 sequentially disposed on an inner surface of the second substrate 71. The organic emitting layer 87 includes red (R), green (G) and blue (B) organic emitting layers 87a, 87b and 87c in the respective sub-pixel regions “SP”. The second electrode 90 is disposed in each sub-pixel region “SP”. A passivation layer 45 covers the substrate 1 having the driving thin film transistor “Tr” and has a drain contact hole 47 exposing a drain electrode 35. A connection electrode 55 is disposed on the passivation layer 45 in each pixel region “SP” and is connected to the drain electrode 35 through the drain contact hole 47. A connection pattern 91 connects the connection electrode 55 and the second electrode 90 in each sub-pixel region “SP”.
In a gate pad area “GPA” of the non-display area “NA”, a gate pad electrode 11 is disposed at the same layer as the gate electrode 9 and the gate line (not shown). The gate pad electrode 11 is made of the same material as the gate electrode 9. In a data pad area “DPA” of the non-display area “NA”, a data pad electrode 38 is disposed at the same layer as source and drain electrodes 33 and 35 and the data line (not shown) on a gate insulator 14. Gate and data pad electrode terminals 57 and 60 are disposed on the passivation layer 45 and contacts the gate and data pad electrodes 11 and 38 through gate and data pad contact holes 49 and 51, respectively. The gate and data pad electrode terminals 57 and 60 are made of the same material as the connection electrode 55.
To improve interface properties and contact resistivities between the connection electrode 55 and the connection pattern 91 and between the connection pattern 91 and the second electrode 90, the connection electrode 55, the connection pattern 91 and the second electrode 90 are made of the same material. When the second electrode 90 acts as a cathode, the second electrode 90 is made of aluminum (Al) having a low work function. Accordingly, the connection electrode 55 and the connection pattern 91 also are made of aluminum (Al).
When aluminum (Al) is exposed to air, it is corroded. The connection electrode 55, the connection pattern 91 and the second electrode 90 formed of aluminum (Al) are not easily corroded, because they are disposed in the display area “DA” encapsulated by the seal pattern 93. In other words, a space between the first and second substrates surrounded by the seal pattern 93 is under a vacuum condition or filled with an inert gas. However, the gate and data pad electrode terminals 57 and 60, which are made of the same material, i.e., aluminum (Al), as the connection electrode 55, are exposed to air. Accordingly, the gate and data pad electrode terminals 57 and 60 are easily corroded.
Further, the gate and data pad electrodes 11 and 38 are generally made of a material having a low resistivity to prevent signal delay, such as aluminum (Al), aluminum alloy (AlNd), aluminum (Al)/molybdenum (Mo) and aluminum alloy (AlNd)/molybdenum (Mo), they are also easily corroded when they are exposed to air, even when the gate and data pad electrode terminals 57 and 60 are not formed in the gate and data pad areas “GPA” and “DPA”. In particular, even when the gate and data pad electrodes 11 and 38 have a double-layered structure in which a upper layer is made of molybdenum (Mo) and a lower layer is made of either aluminum (Al) or aluminum alloy (Al/Nd), the lower layer can be exposed to air and corroded, because the upper layer may be etched along with the passivation layer 45 in a process of forming the contact holes 47, 49 and 51.